The MAC-hs (medium access control-high speed) packet scheduler can operate in two different regions.
Feasible load region: The MAC-hs packet scheduler is able to fulfill the guaranteed bit rate (GBR) requirements for all the allocated High-Speed Downlink Packet Access (HSDPA) users in the cell. Note that the GBRs can be interpreted as minimum target bit rate for some users, like best effort users.
Congested mode: The MAC-hs packet scheduler is not able to fulfill the guaranteed bit rates for all the allocated HSDPA-users. Whether GBR is set as real guaranteed bit rate or the minimum/target bit rate is irrelevant in this context.
The MAC-hs scheduler is expected to operate in the feasible load region which is ensured by Quality of Service (QoS) aware Admission Control (AC) and Load Control (LC); e.g. possible convergence of the Packet Scheduler (PS) is ensured over longer time. However instantaneous congestion will be experienced following the fast changing dynamics (due to e.g., user mobility, user location distribution in cell, and/or non static environment). A characteristic of many of the well-known and QoS-aware packet scheduler methods (including the barrier function packet scheduler as well as the Nokia required-activity-detection scheduler) is that when the scheduler is working in the congested area (also when it is just for a short period), the scheduling is determined primarily by the GBR requirements rather than the channel quality indication (which is the desired goal). However, more elaborate consideration of both characteristics of each user provides significant performance benefits over just using basic scheduling approaches and conduct the sorting. This has been seen in earlier studies (basic user filtering or so-called credit-system approaches which are implemented effectively as a two-step process with first hard and then soft prioritization). In this sense, the MAC-hs scheduling candidate set (SCS) is the set of HSDPA-users who are potential candidates to be scheduled in the next Transmission Time Interval (TTI). When the MAC-hs packet scheduler operates in the feasible load region, the SCS includes all the HSDPA-users that have data in their MAC-hs buffer and/or pending retransmissions in the Hybrid Automatic Repeat Request (HARQ) manager. If the MAC-hs scheduler starts to operate in the congested load region, the SCS could be modified by removing a certain number of users from the SCS until the scheduler can serve all the remaining HSDPA-users in the SCS. Which users and how many users to filter out from the SCS is a non trivial issue since it depends on the number of users with data buffered, on other user's QoS requirements, on the user's channel conditions and sustainable data rate.
In an earlier patent application “QoS-Aware Radio Resource Management (for Wireless Communication) With Activity Detection,” it was found that by dynamically monitoring the scheduled transmit data rate as well as the required data rate from a QoS perspective, significant scheduling gain could be achieved over well-known reference schedulers from the open literature.